In known systems for high-throughput wireless transmissions, which can be used especially in a domestic environment, the signals sent by the transmitter reach the receiver along a plurality of separate paths. At the receiver, this results in interference capable of causing fading and distortions of the transmitted signal and consequently a loss or deterioration of the information to be transmitted. To overcome this drawback, directional antennas of the horn, reflector or array type are usually used, these antennas being used for transmission and/or reception and making it possible to combat or attenuate the deterioration related to multiple paths. Specifically, apart from the gain afforded by the directional antenna, the latter makes it possible, by spatial filtering, on the one hand to reduce the number of multiple paths, and hence to reduce the amount of fading, and on the other hand to reduce the interference with other systems operating in the same frequency band.
Since directional antennas do not allow significant azimuthal spatial coverage, French Patent No. 00 15715 filed in the name of the applicant therefore proposed a compact sectorial antenna based on Vivaldi-type antennas. This antenna consists of a “centrifuge” circular arrangement of n Vivaldi-antenna-type printed radiating elements (n being an integer greater than 2), making it possible to present several directional beams sequentially over time. The set of beams provides complete 360° coverage of space.
The switching operation is carried out by virtue of a switch external to the antenna. In general, this switch consists of diodes combined with power-adder/divider circuits and control electronics comprising at least n ports, making it possible to select one or more Vivaldi antennas from the n elements. To ensure acceptable performance in terms of matching, more than one diode is often used on each port. Furthermore, losses from the power-adder/divider circuits are added to the coupling losses of the slotline-microstrip line transition needed for exciting Vivaldi antennas. Finally, the diode state (on or off) is controlled by bias voltages. In order to be able to isolate the voltages provided on each port, circuits blocking the DC current (DC block) are used. These introduce additional losses.
Thus this switching function is often expensive as a result of the price of diodes and the production costs and bulky because of the biasing circuits and the power-adder/divider circuits. Moreover, it introduces not inconsiderable power losses: losses in the divider/adder circuits, losses due to the DC-block and losses in the diodes. These losses result, on reception, in an increase in the noise temperature of the receiver and, on transmission, in a dry loss of the power to be transmitted, which requires overdimensioning of the power amplifier, which may present a very significant additional cost.